Re: Accessing ControlLogix PLC program tags with EtherIP

[Kay-Uwe Kasemir <kasemirk@ornl.gov>]

On Oct 12, 2005, at 13:21 , Mike Forster wrote:
> I couldn't find this path information previously on tech-talk and it
> may prove useful to others using the EtherIP driver.
>
> To access a program tag on the controller use:
> Program:[Program name].[tag name]
>
> such as:
> Program:Magnet_control.magnet1_value

Hi Mike:

The thing is that the driver/device support
was based on documentation from AllenBradley.
Their document "Logix5000 Data Access",
1756-RM005A-EN-E,
a copy of which is available on
on http://ics-web1.sns.ornl.gov/~kasemir/etherip
states explicitly (page 4):

"Logix5000 tags have these properties:
 * name ... up to 40 characters"

Gee wiz, they copied the EPICS 40 char string
limitation!!

"* scope:
– controller (i.e., global), which you can access directly
– program (i.e., local), which you can not access via an
external device"

So by definition, access to program tags is
impossible.
We should thus add this to the list of
quirks we love about Allen Bradley ;-)

Thanks,
-Kay